Comprehensive Study on Curing, Plugging, and Acid-Dissolution of Antipollution MgO-Based Curing Material in Polysulfonate Drilling Fluid

Direct injection of low-solid curable materials with drilling fluid has the potential to streamline the construction process and reduce costs associated with lost circulation. In this paper, the basic properties, curing behavior, plugging performance, and acid-dissolution characteristics of the mixed slurry using self-made Magnesium oxide (MgO)-based curing material (MCM) combined with polysulfonate drilling fluid were investigated. The basic properties of the mixed slurry exhibited excellent pollution resistance of MCM. The mixed slurry containing 30–50% MCM showed the volume shrinkage ranging from −1.55% to 3.02% and the curing time spanning from 1.67 hours to 2.17 hours, showing exceptional curing behavior. The drilling fluid had no effect on the final strength, but the different components had either negative [sulfonated phenolic resin (SMP-1)] or positive [sodium hydroxide (NaOH)] effects on the hydration process through scanning electron microscope (SEM), X-ray diffraction (XRD), and energy-dispersive spectrometer (EDS). Besides, retarder effectively extended the curing time to 270–470 minutes without compromising the strength of the final cured product or affecting formation processes, which can be used to control the curing time of MCM. Pressure-resistance testing revealed that sealing zones and induced cracks with rough surfaces exhibited higher interfacial bonding capacity, while induced cracks as small as 2 mm showed minimal leakage at pressures up to 16 MPa and eventually stabilized at 14 MPa. Furthermore, acid dissolution tests demonstrated complete release of cured products in a short time, offering potential benefits for reservoir protection. Field application examples further confirmed the compatibility of MCM with drilling fluid and its effectiveness in sealing cracks.